Calcium aluminosulfate and expansive cements containing same



BOG-B9 U ed CEMENTS CONTAINING SAME CALCIUM ALUMINOSULFATE AND EXPANSIVEThis invention relates to expansive cement compositions. 1

Portland cement is prepared by mixing together limestone and anargillaceous material, grinding the mixture to a fine powder, thenputting the ground material through a kiln at a temperature of incipientfusion to form a clinker, which is then ground, together with a smallamount of gypsum, into a fine powder. Chemically, Portland cementconsists primarily of calcium silicates, principally tricalcium silicateand generally a smaller amount of beta dicalcium silicate together withlesser quantities of tricalcium aluminate and tetra calciumaluminoferrite, also minor quantities of alkalies and magnesia. Uponadmixture with water the cement hydrates, sets and hardens and serves asa binder for sand, gravel or other mineral aggregates.

As is well known, concrete made fro Portland cement, together with sand,gravel or other mineral aggregate, undergoes undesirable shrinkage ondrying. This shrinkage is disadvantageous, among other reasons, becauseunder conditions of restraint it generally gives rise to cracks in theconcrete.

Efforts have been made heretofore to produce cement which will notshrink and which car 1 be aglgled tg ljgrt- 1a n d.,crnentor used inplaceo'f'PbTtland cement to pro-' vide nonshrinking concrete. (Bynonshrinking is meant that no net shrinkage occurs, although at somestage or other shrinkage may occur.)

As an example, inorganic cementitious compounds have been prepared whichare expansive. That is to say, when such a compound is mixed with sand,gravel or other mineral aggregate and water and the mixture is allowedto set and cure, a net expansion occurs. By adding such an expansivecomponent in suitable proportion to Portl-and cement it is possible tocompen ate in some degree,

or entirely, for the normal shrinkage of Portland cement concretes.

This concept has been carried to the point of adding enough expansivecomponent to Portland cement to produce a net expansion. That is to say,the blended expansive cement will undergo expansion rather thancontraction during early ages of hydration and even under subsequentdrying conditions. Such expansion has an important advantage, namely,that with adequately high expansions it is possible to bring aboutself-stressing of steel reinforcing members embedded in concrete andconsequent prestressing of the concrete itself without the use ofmechanical stressing methods.

As is well known, the structural strength of reinforced concrete and themechanical properties of concrete structural elements are improved bystressing the steel reinforcement members, such being generallyaccomplished by thermal or by mechanical means, for example, by pullingupon steel reinforcement cables, rods or the like to place them intension before the concrete has set and cured. When the pulling force isrelieved the tension in the steel reinforcement members places theconcrete in compression and, as a result, the concrete has greaterstrength and considerably greater resistance to loading conditions whichproduce tension in structural members. Also post tensioning of steel ispracticed.

However, there are many situations where it is incon- States Patentvenient or where it is impossible to carry out either thermal ormechanical postor pre-stressing, particularly where three dimensional orvolume prestressing is desired. Therefore, if a cement is prepared whichis of the expansive variety and which will produce a sufficiently highnet expansion of the finished concrete product, such expansion willcause stressing of appropriately anchored steel reinforcing members, andit is, therefore, applicable to situations where conventional mechanicalstressing or thermal stressing is impossible or diflicult oruneconomical, for example, concrete pipe, large highway slabs and caseswhere three dimensional stressing is desired.

Nevertheless, nonshrinking cements and self-stressing expansive cementsas provided heretofore have had certain serious disadvantages. Certainof these cements have required a high degree of care during the curingperiod, and/ or have required an excessively high ratio of cement toaggregate and/ or the further addition of control agents to controlexpansion rates and magnitudes. The so-called Lossier cements, which areexpansive cements, require the presence of a terminator, such as blastfurnace slag, which is disadvantageous because of added cost, theinconvenience of multi-component systems, the presence of an additionalfactor requiring control and the inability to predict the ultimatemagnitude and rate of expansion. Also, the Lossier cements have a lowdegree of expansion and have been found to be inadequate for purposes ofselfor chemical prestressing.

It is an object of the present invention to provide improvements in theart of expansive cements and in the expansive components of suchcements.

It is a particular object of the invention to provide an expansivecementitious material having a high degree of expansion such that theaddition of a quantitatively minor portion thereof to a quantitativelymajor portion of Portland cement will produce a blended cement which issufliciently expansive to bring about self-stressing of steelreinforcement and tensioning members.

Yet another object of the invention is to provide expansive cementshaving a high degree of expansion and which do not require the presenceof a terminator or other additions to regulate the rate or magnitude ofexpansion.

The above and other objects of the invention will be apparent from theensuing description and the appended claims.

For convenience of further description, certain symbols prevalent in thecement technology will be used from time to time as follows: Calciumoxide (CaO) is represented as C; aluminum oxide (A1 0 as A; silica (SiOas S, and sulfur trioxide ($0 as 5 Where extractable lime is indicated,it will be referred to as extractable lime or free CaO to distinguish itfrom unextractable or bound calcium oxide (C). By extractable lime orfree CaO" is meant lime extracted by the method of ASTM Cll4-58.

In accordance with my invention, a clinker is prepared which is high inextractable lime or free CaO as defined above, the remainder of which ispredominantly or en-' tirely Me. This clinker, and the cement blend towhich it is a ded as the expansive component, contain no addedterminator or, if such is added, it is added in an amount which does notsignificantly alter the expansive hydration of the cement.

I have found that by observing certain conditions a clinker is producedwhich is superior as a component of expansive cements to clinkerspreviously produced including those described in an article by myselfand G. E. Troxell appearing in Proceedings of the American Society forTesting Materials, vol. 58 (1958), pages 986-1008.

More specifically, I start with suitable source materials for C, A and Ssuch as calcium carbonate, alumina and EXA M i ii iii Q gypsum; I mixthem in proportions to produce a clinker having the formula C A +d (freeCaO) wherein the molecular coefiicients a, b, c and d are as describedbelow; and I burn this mixture at a temperature sufiicient to form aclinker but not above incipient fusion and in no case above about 2900F.

There results from such procedure a clinker having the formula expressedabove in which, taking as unity -(i.e., one mole of S 11 has theapproximate value of 1 to 4, b has the approximate value of 1 to 3 and dhas the approximate value of 1 to 2. Moreover tl 1e t ot al amount offree CaO ranges from abop t 21 to 40% gf tge wHghfiTfflTe c m er.

Ilils cliikel'haTariifidex of refraction of about 1.56 to 1.59. TheX-ray diffraction pattern of the clinker shows spacings, including thoseof maximum intensities, of 4.90, 3.75, 3.49, 3.24, 2.90, 2.65 and 2.16.This order does not indicate the order of maximum intensities, since thevalues of maximum intensity will vary from case to case depending uponminor constituents which may reinforce or tend to cancel particularspacings.

Further criteria are as follows: Free CaSO as determined by the methodof Forsen using saturated lime water (described in A.C.I. Journal, vol.31, January 1960) is not more than 5% by weight based on the clinker.The sum of free CaO and S0 exceeds about 37% by weight based on theclinker. The weight ratio of (free CaO+SO to (total CaO+Al O +SO exceedsabout 0.38. The total CaO-l-Al O +SO exceeds about 75% of the weight ofthe chlinker. With the above, where Al O is referred to, TiO isexcluded. All methods of determination involved are in accordance withASTM C114-58 specifications for analysis of Portland cement, except freeCaSO which is determined by the method of Forsen, as stated.

It has been verified by analytical procedures such as those described ina paper by Halstead and Moore, The Composition and Crystallography of anAnhydrous Calcium Aluminosulphate Occurring in Expanding Cement, Journalof Applied Chemistry, volume 12, pages 413- 417 (1962), and in a paperby Fukuda in Journal of Ceramic Association of Japan, volume 69 (1961),entitled Investigation of Compound Compositions of Sulpho-AluminousCement, that the calcium sulpho-aluminate prepared by the method hereindescribed is a stable compound and that it has the formula C A Thefollowing specific examples will serve further to illustrate thepractice and advantages of my invention.

EXAMPLE 1 Preparation of Clinker A] An intimate, finely divided raw mixwas prepared as follows, percentages being by weight.

Percent Commercial grade, ground calcium carbonate (whiting) 51.7Commercial grade gypsum 31.3 Commercial grade hydrated alumina 17.0

Total 100.0

These ingredients, as indicated, were of commercial grade such as couldbe used in the commercial manufacture of Portland cement. e mix was madeinto a thin past into a paste, spread, etc. In either case, theresulting squares are placed in an electric furnace and heated toincipient fusion (2570 F.).

The resulting clinker had the following analysis:

Clinker A-I Analysis Percent CaO (total) 54.4 A1 0 25.6 S0 18.4 SiO 0.76Fe O 0.28 MgO 0.43 TiO 0.01 Loss on ignition 0.47

By chemical analysis it was determined that Clinker A-1 contained 23.2%free CaO and 1.1% free CaSO All chemical analyses except thedetermination of free CaSO were by the methods of ASTM C114-58. The freeCaSO determination was by the method of Forsen using saturated limewater as an extractant, as described by Toshio Manabe in Determinationof Calcium Sulfoaluminate in Cement Paste by Tracer Technique, ACIJournal, vol. 31, No. 7, January 1960.

From the above data (A) free CaO plus S0 was found to be 41.6%; (B) thesum of C20, A1 0 (excluding TiO and S0 was found to be 98.4%; and (C)the ratio of A to B was found to be 0.423. For convenience and to avoidrepetition in the following examples, these quantities will be referredto as A, B and C, respectively.

EXAMPLE 2 Preparation of C linker C-4 This clinker was prepared by thesame procedure as that of Example 1 but from a raw mix as follows,percentages by weight:

Percent Industrial high grade limestone 48.5 Commercial grade gypsum28.7 South American bauxite 22.8

Total 100.0

The temperature of incipient fusion was 2470 F. Analysis of Clinker C-4was as follows:

Free lime was 23.5% and free CaSO was 1.9%, determined by the methodsreferred to in Example 1. The values of A, B and C were 42.5%, 96.6% and0.440, respectively.

EXAMPLE 3 Preparation of Clinker B4 In this example,

rotary kiln fired with fuel oil and high pressure air wamm of [wt icing?and the ground raw mix was nodulize by application f a water spray in arotating drum mixer and screening to yield a kiln feed between /2 inchand a No. 4 sieve. The raw mix was as follows, percentages by weight:

Percent Commercial grade, ground calcium carbonate (whiting) 48.7Commercial grade gypsum 28.7 South American bauxite 22.6

Total 7.00.0

Analysis of Clinker B-4 was as follows:

Free CaO and free CaSO determined as described in Example 1, were 22.9%and 2.2%, respectively. The values of A, B and C were 40.3%, 96.2% and0.419, respectively.

EXAMPLE 4 Testing of Expansive Compositions A-I, B4 and C-4(Unrestrained Prisms) 1 Each of the above clinkers (A-l, C-4 and B-4)was ground to a suitable fineness (between 2500 and 3000 e er the M suare centimeters per gram as y mming proportions with a commercial ASTMType I Portland cement having between 53 and 57% tricalcium silicatecontent but otherwise meeting specifications for ASTM Type II Portlandcement. Each blend of expansive cement (Clinker A-l, C-4 or B-4) andPortland cement was mixed with an aggregate and water and cast intoprisms as follows:

The aggregate was a mixture of 40% sand and 60% clean river gravel ofinch maximum size. The cement factor was 8 sacks of blended cement percubic yard of finished concrete. Water was added in the proportion of31% by weight of blended cement. The mix had a slump of l to 2 inches bythe method of ASTM Cl43-58. The wet mix was cast, using light vibration,into 2" x 2" x 12" molds (inside dimensions). The set prisms werestripped at eight hours. Initial length measurements were made at thattime and the prisms were then cured in fog at 70 F and at 100% relativehumidity. Observations of length change were made daily. Results are setforth in Table I below:

TABLE I (1) Expansive component of blended cement A-l C4 (3-4 B-4 B-4B-4 (2) Amount of expansive component (percent by wt. of

total cement) 25 20 25 Expansions, expressed as percent change of lengthAge of curing, days alter ing reinforcement steel in a manner torestrain the prisms during curing, the expansive reaction producedtensile stresses in the steel and consequent compressive stress of theconcrete. The following example illustrates the prestressing ofreinforcement steel.

EXAMPLE 5 Testing of Reinforced Prisms Concrete mixes were prepared asin Example 4 with the cement blends therein described and the wet mixeswere cast into prisms, but steel reinforcement rods equal in crosssection to 1.1% of the cross section of the prisms were applied in arestraining mechanism external to the prisms immediately after strippingthe prisms from the molds. That is to say, the steel was not embedded inthe concrete but was attached to a restraining mechanism such thatexpansion of the prisms would be imparted to the steel causing stressingof the steel. Results were as set forth in Table II below:

TABLE II (2) Sell stress, p.s.i., (1) Amount Maximum Age at at time ofmaxi- Expansive of (1) expansion, maximum mum expansion Component(percent percent expansion oi Cement by wt. oi change of (days) totallength Steel Concrete cement) In the expansive cement components of thepresent invention, alumina (A1 0 is a preferred constituent but 1 it maybe substituted in part or in whole by other sesqui- I oxides such as CrO Mn O Fe O and V 0 It will, therefore, be apparent that'expansivecement components are provided which, when blended with regular Portlandcement in minor proportions, cause substantial expansion of concretemade from the blends, and that the prestressing of steel is madepossible, all without the need to add a terminator.

Moreover, by means of my invention, it is possible to control (1) themagnitude of expansion and (2) the rate of expansion. Such control will,of course, depend upon various factors such as (a) the Portland cementcontent, (b) the water-to-cement ratio and (c) the selection ofexpansive component. But with such factors being given, it is possible,by controlling the proportion of expansive component, to control themagnitude and rate of expan sion. For example, referring to Table Ihereinabove, it will be seen that by using 20, 25 or 30% of Clinker B-4expansions (unrestrained) of 3.5, 4.4 and 8.9%, respec tlvely, wereachieved and that the rates of expansion varied considerably, being muchgreater with a 30% addition than with 20 and 25% additions. Referring toTable II, it will be seen that in the case of restrained prisms withreinforcement steel, similar control (greater magnitude and greaterrate) are achieved with the same clinker (B-4) using larger proportionsof this expansive component. It will be understood by those skilled inthe art that the ability to control (as well as to achieve) themagnitudes of expansion and/ or of self-stressing, and to control therates thereof, is a great advantage.

This invention is directed primarily to the production of expansivecement blends which have a substantial degree expansion, e.g., 1% ormore in unrestrained condition when mixed with water and aggregate andallowed to cure. However, in its broader aspects, by invention alsoincludes cement blends which are non-shrinking without being expansive,or which are expansive but have a low degree of expansion. That is tosay, the present invention, in its broader aspects, includes cementblends which Y are not expansive but which do not shrink, and itincludes cement blends which are expansive but only to a slight extent,e.g., not greater than about 1%, when mixed with aggregate and water andallowed to cure in unrestrained condition. For example, my novelexpansive components such as the above described Clinkers Al, C4 and B4,or the expansive components of the above-mentioned Klein and Troxellarticle may be blended with Portland cement in an amount sufficient toproduce a nonshrinking blend or a blend having a low degree ofexpansion, such blends being devoid of terminators or containing terminator in an amount which is not significant.

It will, therefore, be apparent that new and useful ex- 1. A calciumaluminosulfate of the formula C A +d (free CaO) wherein a, b, c and dare molecular coefiicients having values of about 1 to 4, l to 3, 1 and1 to 2, respectively; C, A and g are bound CaO, bound A1 and bound S0respectively; the free CaO is extractable by the method of ASTM'C114-58; the product is formed by heating a mixture of a source of CaO,a source of A1 0 'and a source of S0 to a temperature not exceeding thetemperature of fusion but sufiicient to form a clinker; said producthaving an index of refraction of about 1.56 to 1.59; having free CaSO bythe method of Forsen not greater than 5%; having a combined CaO-l-SOcontent exceeding about 37%; having a weight ratio of free CaO+SO tototal CaO+Al O +SO exceeding about 0.38; and having a total CaO+Al O +SOcontent exceeding about 75%.

2. A cement composition consisting essentially of a major proportion ofPortland cement and a minor proportion, sufficient at least tocompensate for shrinkage of the Portland cement, of an expansivecomponent, said expansive component being derived by burning, at atemperature not above about 2900 F., a mixture of a source of CaO, of Xand of S0 wherein X is a sesquioxide selected from the group consistingof A1 0 Fe O Cr O Mn O and V 0 said expansive component consistingessentially of (1) a stable compound in the form of a calcium aluminosulphate type of compound (2) associated CaO extractable by the methodof ASTM Cl1458 and (3) associated anhydrous CaSO extractable by themethod of Forsen, said calcium alumino sulphate type of compoundaccounting for the major portion by weight of said expansive component,said associated CaO being present in amount sufiicient to impartsubstantial expansive properties to the expansive component when it ishydrated, said associated anhydrous CaSO being present not in excess ofabout 5% of the expansive component, said composition beingsubstantially free of added terminator.

3. The cement composition of claim 2 wherein X is A1 0 4. The cementcomposition of claim 3 wherein said associated CaO exceeds 21% by weightof the expansive component.

5. A cement composition consisting essentially of a major proportion ofPortland cement and a minor proportion, sufficient at least tocompensate for shrinkage of the Portland cement, of an expansivecomponent, said expansive component being a solid ternary systemconsisting essentially of (1) the anhydrous compound wherein X is asesquioxide selected from the group consisting of A1 0 R 0 Cr O Mn O andV 0 (2) C210 extractable by the method of ASTM C11458, and (3) CaSO,extractable by the method of Forsen, said ternary system containingsufiicient of said extractable CaO to cause substantial expansion ofsaid expansive component when it is hydrated and containing not morethan about 5% of said extractable CaSO, based on the weight of saidexpansive component, said cement composition being substantially free ofadded terminator.

6. The cement composition of claim 5 wherein X is A1 0 7. The cementcomposition of claim 6 wherein the extractable CaO exceeds 21% by weightof the expansive component.

8. An expansive material adapted to be added to Portland cement to atleast compensate for shrinkage thereof, said expansive material being inthe form of the burned product of a mixture of a source of CaO, of X andof S0 wherein X is a sesquioxide selected from the group consisting ofA1 0 Fe O Cr O Mn O and V 0 said burned product being formed by burningat a temperature not substantially greater than 2900 F. and consistingessentially of a ternary system having, as the major comp0- nent byweight, a calcium alumino sulphate type of compound, and having as theother components CaO extractable by the method of ASTM Cl14-58 andanhydrous CaSO extractable by the method of Forsen, said extractable CaObeing in excess of 21% of the weight of expansive material, saidanhydrous CaSO being present not in excess of about 5% of the weight ofsaid expansive material.

9. The expansive material of claim 8 wherein X is A1 0 References Citedin the file of this patent FOREIGN PATENTS Great Britain Aug. 15, 1947Canada July 22, 1952 OTHER REFERENCES

1. A CALCIUM ALUMINOSULFATE OF THE FORMULA CAABSC+D (FREE CAO) WHEREINA, B, C AND D ARE MOLECULAR COEFFICIENTS HAVING VALUES OF ABOUT 1 TO 4,1 TO 3, 1 AND 1 TO 2, RESPECTIVELY; C, A AND $ ARE BOUND CAO, BOUNDAL2O3 ARE BOUND SO3, RESPECTIVELY; THE FREE CAO IS EXTRACTABLE BY THEMETHOD OF ASTM C114-58; THE PRODUCT IS FORMED BY HEATING A MIXTURE OF ASOURCE OF CAO, A SOURCE OF AL2O3 AND A SOURCE OF SO3 TO A TEMPERATURENOT EXCEEDING THE TEMPERATURE OF FUSION BUT SUFFICIENT TO FORM ACLINKER; SAID PRODUCT HAVING AN INDEX OF REFACTION OF ABOUT 1.56 TO1.59; HAVING FREE CASO4 BY THE METHOD OF FORSEN NOT GREATER THAN 5%;HAVING A COMBINED CAO+SO3 CONTENT EXCEEDING ABOUT 37%; HAVING A WEIGHTRATIO OF FREE CAO+SO3 TO TOTAL CAO+AL2O3+SO3 EXCEEDING ABOUT 0.38; ANDHAVING A TOTAL CAO+ALIO3+SO3 CONTENT EXCEEDING ABOUT 75%.
 2. A CEMENTCOMPOSITION CONSISTING ESSENTIALLY OF A MAJOR PROPORTION OF PORTLANDCEMENT AND A MINOR PROPORTION, SUFFICIENT AT LEAST TO COMPENSATE FORSHRINKAGE TO THE PORTLAND CEMENT, OF AN EXPANSIVE COMPONENT, SAIDEXPANSIVE COMPONENT BEING DERIVED BY BURNING, AT A TEMPERATURE NOT ABOVEABOUT 2900*F., A MIXTURE OF A SOURCE OF CAO, OF X AND OF SO3, WHEREIN XIS A SEQUIOXIDE SELECTED FROM THE GROUP CONSISTING OF AL2O3, FE2O3,CI2O3, MN2O3 AND V2O3, SAID EXPANSIVE COMPONENT CONSISTING ESSENTIALLYOF (1) A STABLE COMPOUND IN THE FORM OF A CALCIUM ALUMINO SULPHATE TYPEOF COMPOUND (2) ASSOCIATED CAO EXTRACTABLE BY THE METHOD OF ASTM C114-58AND (3) ASSOCIATED ANHYDROUS CASO4 EXTRACTABLE BY THE METHOD OF FORSEN,SAID CALCIUM ALUMINO SULPHATE TYPE OF COMPOUND ACCOUNTING FOR THE MAJORPORTION BY WEIGHT OF SAID EXPANSIVE COMPONENT, SAID ASSOCIATED CAO BEINGPRESENT IN AMOUNT SUFFICIENT TO IMPART SUBSTANTIAL EXPANSIVE PROPERTIESTO THE EXPANSIVE COMPONENT WHEN IT IS HYDRATED, SAID ASSOCIATEDANHYDROUS CASO4 BEING PRESENT NOT IN EXCESS OF ABOUT 5% OF THE EXPANSIVECOMPONENT, SAID COMPOSITION BEING SUBSTANTIALLY FREE OF ADDEDTERMINATOR.